Identification of key subsystems for urban rail vehicles is important for the selection of maintenance strategy. The fuzzy comprehensive evaluation technique is applied to determine the key subsystems of urban rail vehicles. Firstly, the vehicle is divided into nine subsystems according to the module partition method. Then, the degrees of occurrence, severity, detection and maintenance cost are chosen as the evaluation factors that are quantified based on fuzzy theory and collected historical data. Finally, the calculation model of critical degree is established based on the fuzzy comprehensive evaluation method. The proposed approaches are applied to Guangzhou Metro Corporation, and five key subsystems are selected. The experiment results, which are consistent with those of most knowledgeable engineers and experts, indicate the validity of the proposed method.